1. Field of the Invention
The present invention refers to a cutting or drilling apparatus adapted to be driven to rotational movement, in particular to an apparatus receiving a cutting tool or a drilling tool to make holes of a predetermined depth and/or diameter in a workpiece. It is a frequent problem to make a hole or a blind bore having an exactly predetermined depth in a workpiece. If one uses a hand operated drill without any depth stop, it is a difficult task to make a blind bore with the exactly required depth. On the other side, if one uses a conical cutting tool to effect a hole in e.g. sheet metal, it may be very difficult to perform the hole with exactly the required diameter.
2. Prior Art
U.S. Pat. No. 4,039,266, O'Connell, of Aug. 2, 1977 discloses a longitudinal cutting tool comprising a stop collar received on said cutting tool. The stop collar has a stop surface and may be slided and fixed along the cutting tool to determine the depth by which the cutting tool, e.g. a drilling tool, may penetrate a workpiece. Thereby, it is certainly possible to make blind bores of an exactly predetermined depth in a work piece, but everytime you want to change the depth, you have to measure the distance between the tip of the drilling tool and the stop surface and to readjust the stop collar carefully to achieve the desired depth. Moreover, you will need a screwdriver or the like tool to readjust the stop collar and to fix it again. Such stop collars of the prior art may not be used at all with conically shaped cutting tools, e.g. as they are used to cut a circular hole into a sheet metal workpiece. It is well known to anybody skilled in the art that the diameter of the hole in the workpiece strictly depends from the penetration depth of such a conical cutter into the workpiece. It is further of paramount importance to guide the conical tool exactly in a right angle to the workpiece to ensure that the resulting hole is perfectly circular and to avoid a blocking of the tool. As these cutting tools are not of cylindrical shape, the known stop collars may not be used and one has no other choice than to guide the tool by free hands. The result may be that the hole is not perfectly round and that the desired diameter is not attained as exactly as would be expected.